고체역학 (Gere) — Stresses in Beams (Basic Topics): Problem 5.9-5

5.9-5 A sign for an automobile service station is supported by two aluminum poles of hollow circular cross section, as shown in the figure. The poles are being designed to resist a wind pressure of 3.8 kPa against the full area of the sign. The dimensions of the poles and sign are \(h_1 = 7\text{ m}\), \(h_2 = 2\text{ m}\), and \(b = 3.5\text{ m}\). To prevent buckling of the walls of the poles, the thickness \(t\) is specified as one-tenth the outside diameter \(d\). (a) Determine the minimum required diameter of the poles based upon an allowable bending stress of 52 MPa in the aluminum. (b) Determine the minimum required diameter based upon an allowable shear stress of 14 MPa.